Effect of ecdysone receptor gene switch ligands on endogenous gene expression in 293 cells

Hyperoxia-induced hypertrophy and ion channel remodeling in left ventricle

Ventricular arrhythmias account for high mortality in cardiopulmonary patients in intensive care units. Cardiovascular alterations and molecular-level changes in response to the commonly used oxygen treatment remains unknown. In the present study we investigated cardiac hypertrophy and cardiac complications in mice subjected to hyperoxia. Results demonstrate that there is a significant increase in average heart weight to tibia length (22%) in mice subjected to hyperoxia treatment vs. normoxia. Functional assessment was performed in mice subjected to hyperoxic treatment, and results demonstrate impaired cardiac function with decreased cardiac output and heart rate. Staining of transverse cardiac sections clearly demonstrates an increase in the cross-sectional area from hyperoxic hearts compared with control hearts. Quantitative real-time RT-PCR and Western blot analysis indicated differential mRNA and protein expression levels between hyperoxia-treated and control left ventricles for ion channels including Kv4.2 (-2 ± 0.08), Kv2.1 (2.54 ± 0.48), and Scn5a (1.4 ± 0.07); chaperone KChIP2 (-1.7 ± 0.06); transcriptional factors such as GATA4 (-1.5 ± 0.05), Irx5 (5.6 ± 1.74), NFκB1 (4.17 ± 0.43); hypertrophy markers including MHC-6 (2.17 ± 0.36) and MHC-7 (4.62 ± 0.76); gap junction protein Gja1 (4.4 ± 0.8); and microRNA processing enzyme Drosha (4.6 ± 0.58). Taken together, the data presented here clearly indicate that hyperoxia induces left ventricular remodeling and hypertrophy and alters the expression of Kv4.2 and MHC6/7 in the heart.

Selenoprotein P regulation by the glucocorticoid receptor

Maintenance of the antioxidant activity of selenoproteins is one potential mechanism of the beneficial health effects of selenium. Selenoprotein P is the primary selenium distribution protein of the body as well as the major selenium containing protein in serum. The transcriptional regulation of selenoprotein P is of interest since the extrahepatic expression of this gene has demonstrated differentiation-dependent expression in development as well as under different disease states. SEPP1 displays patterned expression in numerous tissues during development and the loss of SEPP1 expression has been observed in malignancy. In addition, factors that influence inflammatory processes like cytokines and their regulators have been implicated in selenoprotein P transcriptional control. Herein, we identify a retinoid responsive element and describe a mechanism where the glucocorticoid receptor negatively regulates expression of selenoprotein P. Luciferase reporter assays and quantitative PCR were used to measure selenoprotein P transcription in engineered HEK-293 cells. When stimulated with ecdysone analogs, selenoprotein P expression was increased with the use of a fusion transcription factor that contains the glucocorticoid receptor DNA binding domain, an ecdysone ligand-binding domain, and a strong transactivation domain as well as the retinoid X receptor. The native glucocorticoid receptor inhibited selenoprotein P transactivation, and selenoprotein P was further attenuated in the presence of dexamethasone. Our results may provide insight into a potential mechanism by which selenium is redistributed during development, differentiation or under conditions of critical illness, where glucocorticoid levels are typically increased.

Controlled expression of functional miR-122 with a ligand inducible expression system

Background

To study the biological function of miRNAs, and to achieve sustained or conditional gene silencing with siRNAs, systems that allow controlled expression of these small RNAs are desirable. Methods for cell delivery of siRNAs include transient transfection of synthetic siRNAs and expression of siRNAs in the form of short hairpins using constitutive RNA polymerase III promoters. Systems employing constitutive RNA polymerase II promoters have been used to express miRNAs. However, for many experimental systems these methods do not offer sufficient control over expression.

Results

We present an inducible mammalian expression system that allows for the conditional expression of short hairpin RNAs that are processed in vivo to generate miRNAs or siRNAs. Using modified nuclear receptors in a two hybrid format and a synthetic ligand, the Rheoswitch system allows rapid and reversible induction of mRNA expression. We evaluated the system's properties using miR-122 as a model miRNA. A short hairpin encoding miR-122 cloned into the expression vector was correctly processed to yield mature miRNA upon induction with ligand and the amount of miRNA produced was commensurate with the concentration of ligand. miR-122 produced in this way was capable of silencing both endogenous target genes and appropriately designed reporter genes. Stable cell lines were obtained, resulting in heritable, consistent and reversible expression of miR-122, a significant advantage over transient transfection. Based on these results, obtained with a microRNA we adapted the method to produce a desired siRNA by designing short hairpins that can be accurately and efficiently processed.

Conclusion

We established an Inducible expression system with a miR-122 backbone that can be used for functional studies of miRNAs and their targets, in heterologous cells that do not normally express the miRNA. Additionally we demonstrate the feasibility of using the miR-122 backbone to express shRNA with a desired siRNA guide strand for inducible RNAi silencing.

Effect of PTTG on endogenous gene expression in HEK 293 cells

Background

Pituitary tumor transforming gene (PTTG), also known as securin, is highly expressed in various tumors including pituitary, thyroid, colon, ovary, testis, lung, and breast. An overexpression of PTTG enhances cell proliferation, induces cellular transformation in vitro, and promotes tumor development in nude mice. PTTG also inhibits separation of sister chromatids leading to aneuploidy and genetic instability. A great amount of work has been undertaken to understand the biology of PTTG and its expression in various tumors. However, mechanisms by which PTTG mediates its tumorigenic function are not fully understood. To utilize this gene for cancer therapy, identification of the downstream signaling genes regulated by PTTG in mediation of its tumorigenic function is necessary. For this purpose, we expressed PTTG in human embryonic kidney (HEK293) cells that do not express PTTG and analyzed the downstream genes using microarray analysis.

Results

A total of 22,277 genes printed on an Affymetrix HG-U133A 2.0 GeneChip™ array were screened with labeled cRNA prepared from HEK293 cells infected with adenovirus vector expressing PTTG cDNA (AdPTTG cDNA) and compared with labeled cRNA prepared from HEK293 cells infected with control adenovirus (control Ad) or adenovirus vector expressing GFP (AdGFP). Out of 22,277 genes, 71 genes were down-regulated and 35 genes were up-regulated with an FDR corrected p-value of ≤ 0.05 and a fold change of ≥2. Most of the altered genes identified are involved in the cell cycle and cell apoptosis; a few are involved in mRNA processing and nitrogen metabolism. Most of the up-regulated genes belong to the histone protein family.

Conclusion

PTTG is a well-studied oncogene for its role in tumorigenesis. In addition to its importance in regulation of the cell cycle, this gene has also been recently shown to play a role in the induction of cell apoptosis. The microarray analysis in the present study demonstrated that PTTG may induce apoptosis by down-regulation of oncogenes such as v-Jun and v-maf and up-regulation of the histone family of genes.

The Karlson Lecture. Phytoecdysteroids: what use are they?

Phytoecdysteroids are analogues of arthropod steroid hormones found in plants, where they deter predation by non-adapted predators. There is potential to exploit this to develop new strategies for pest control, either by using ecdysteroids as lead molecules for the design of novel pest control agents or by alteration of ecdysteroid levels/profiles in crop plants through plant breeding or genetic modification. However, it is other properties of phytoecdysteroids that have led to a rapid recent increase in scientific and commercial interest in these molecules. They are apparently non-toxic to mammals and a wide range of beneficial pharmacological (adaptogenic, anabolic, anti-diabetic, hepatoprotective, immunoprotective, wound-healing, and perhaps even anti-tumour) activities is claimed for them. In particular, this has led to a large (and unregulated) market for ecdysteroid-containing preparations for body-builders, sportsmen, and pets, among others. Ecdysteroids are also being considered as nutraceutical additives to food products. Further, ecdysteroids are good candidates as elicitors for gene-switch systems to be used in medical gene therapy and research applications. In this article, I review the applications of phytoecdysteroids and assess their future potential.